Path: utzoo!news-server.csri.toronto.edu!rutgers!usc!samsung!caen!dali.cs.montana.edu!milton!hayes.ims.alaska.edu!floyd From: floyd@ims.alaska.edu (Floyd Davidson) Newsgroups: comp.dcom.modems Subject: Re: comp.dcom.modems lexicon Message-ID: <1991Mar9.061220.28290@ims.alaska.edu> Date: 9 Mar 91 06:12:20 GMT References: <19594@cbmvax.commodore.com> <1991Mar8.082523.25819@ims.alaska.edu> <19660@cbmvax.commodore.com> Organization: University of Alaska, Institute of Marine Science Lines: 84 In article <19660@cbmvax.commodore.com> grr@cbmvax.commodore.com (George Robbins) writes: >In article <1991Mar8.082523.25819@ims.alaska.edu> floyd@ims.alaska.edu (Floyd Davidson) writes: >> In article <19594@cbmvax.commodore.com> grr@cbmvax.commodore.com (George Robbins) writes: >> >In article <1991Mar7.055236.16871@ims.alaska.edu> floyd@ims.alaska.edu (Floyd Davidson) writes: >> > >> >It's a misuse when all it refers to is enabling and disabling >> >local echo, while the modem is actually still modulating in >> >the full duplex mode. >> >> Not so. See below. (By the way, would you be so kind as to define >> "modulating in the full duplex mode". :-) > >In this case of the Bell 103/113/212 modem, something where you've >said "half/duplex or local echo", but are still using separate >transmit/receive carriers instead of a controlled carrier. I guess you didn't realize the the phrase is utter nonsense. It doesn't mean anything. And your definition doesn't match the phrase, or even close. [...] >> Maybe you will have to blame Ma Bell for that definition. At >> the other end of that teletype loop there is a modem, though it >> was called a Teletype Terminal Unit at the time, which had two >> modes of operation: half duplex and full duplex. In some >> cases, such as the Western Electric 43A1 it had a switch, in >> others it was just wired differently. In either case the modem >> put out an analog transmit signal and received an analog receive >> signal. In other words the modem was "duplex" on the analog side >> no matter what was on the digital side. The fd/hd switch or >> option only affected the digital side. > >This is blatent revisionism. 8-) The original teletype circuit was >a telegraph current loop. The "modems" reflect the adoption of FDM >multiplexing of multiple teletype channels over a single teletype It didn't multiplex multiple teletype channels over a single teletype channel. >or telephone circuit and subsequently use of fairly standard modem >technology to extend teletype services though standard telephone >networks. Revisionism? What are you talking about, "fairly standard modem technology"? It predated the whole idea of a "modem" as you know them. A teletype terminal unit does exactly what you described above as a definition of "modulating in the full duplex mode". It has nothing to do with modulation (or demodulation) modes. It multiplexes 16 teletype channels onto a single voice channel. The earliest TU that I've worked on was the WECO 43A1, which probably was designed in the late '40s. It had *tubes* in it. And the 43A1, and all other TU's that I've worked on (and that is a few...) all have a half/full duplex option. And in all cases the analog side is totally unaffected by which option is in use. The purpose of half/full duplex is to provide local echo operation of the teletype machine. The half/full duplex option affects ONLY the digital side. The idea that half/full duplex had anything at all to do with the analog side of the modem is a relatively recent event. >> (I am sitting six feet from four each eleven foot bays of >> Lenkurt telegraph equipment. Some pretty old 25D stuff, there >> are about 200 modems, all of which have a half/full duplex >> option.) > >Scary! Ah, we agree on something. Except I doubt you really know what is scary about it. Your government still pays money to use them. Now that is scary. (Thats why they still exist.) Floyd -- Floyd L. Davidson | floyd@ims.alaska.edu | Alascom, Inc. pays me Salcha, AK 99714 | Univ. of Alaska | but not for opinions.